This invention relates to improvements in apparatus for dispensing finely divided powders or granular materials and, in particular, to improvements in xerographic toner dispensing apparatus.
More specifically, this invention relates to a xerographic toner container having dispensing means associated therewith that is particularly adapted for use in conjunction with a xerographic developing apparatus. Basically, in the art of xerography, an imaging member formed of a photoconductive surface carried on a conductive substrate is uniformly charged and the surface of the imaging member then exposed to a light image of an original which is to be copied. The photoconductive layer becomes conductive under the influence of the light image to selectively dissipate the charge found thereon thus forming a latent electrostatic image. To make this latent image visible, a finely divided pigmented resin-based material, commonly referred to as toner, is first charged to a potential opposite to that of the latent electrostatic image and then while still in a charged state, brought into contact with the latent image where the charged toner particles are attracted to the image where the charged toner particles are attracted to the image areas. The developer image is usually transferred from the plate surface to a final support material and fixed thereto to form a permanent record of the original.
The resin-based toners employed in the practice of the xerographic process are generally blended from finely subdivided materials to yield an extremely fine powder composition having an average particle size of about 10 microns. As used in most automatic xerographic reproducing apparatus, the fine toner particles are brought into rubbing contact with a triboelectrically remote and relatively coarser "carrier" material. The rubbing or mixing action causes the toner particles to become triboelectrically charged to a polarity opposite that of the carrier. The charged toner particles electrostatically coat themselves on the surface of the coarser carrier material and remain bonded there in a charged state. The two component material is then brought into contact with an image bearing photoconductive plate by one of several known techniques where the toner is electrostatically transferred from the carrier surface to the latent image areas to effect development. As can be seen, the coarser carrier particles not only provide a means for charging the toner material, but also provide a vehicle by which the toner particles are conveniently handled and transported in the xerographic development apparatus.
In order to sustain continuous operation in the automatic device, the toner material consumed in the development process must be periodically replaced within the development system. One arrangement for resupplying spent toner involves the use of a sealed toner cartridge or package which is placed into the xerographic machine when toner is depleted. The package usually includes a series of openings which are covered with an easily removable adhesive strip. The strip is removed from the package while maintaining the opening in the package at a 12 o'clock position. The package is then inserted into a receiving portion of the machine generally above the developer sump and rotated to bring the openings to the 6 o'clock position. This feeds the contents of the package into a dispensing hopper from whence a controllable amount of toner is periodically added to the development system in accordance with an error signal developed in accordance with well known techniques. The package is left in the machine until a new package is needed to fill the hopper.
Dispensing of toner from the hopper of the above described arrangement may be accomplished by means of a toner dispensing foam roll in accordance with U.S. Pat. No. 3,596,807 or Re27,876.
However, it has been found that the apparatus referred to in the above identified patents, while solving the problems heretofore associated with the prior art dispensing devices, has not proven entirely satisfactory for dispensing under all conditions.
More specifically, the foam roll of such toner dispensers is located to block an elongated opening in the dispenser housing, the opening spanning the width of developer housing. While such rolls have the outstanding characteristic of dispensing evenly across the width of the opening, it is sometimes desirable to dispense at a faster rate near the ends of the roll than at the central portion thereof. The above situation may typically be caused by the use of a toner cartridge which has a width greater than the width of the dispensing opening. When toner is dumped into the dispenser from such a cartridge, a greater head of toner is located above the ends of the dispensing roll. If left uncompensated, the low toner indicator located to sense the level of toner near the central portion of the dispenser would be activated prematurely (i.e. when a significant amount of toner was present in the dispenser above the ends of the roll).
In addition, to the general advantages of being able to control the uniformity of dispensing from a resilient open-cell roll dispenser, it is also desirable to control the rate at which dispensation takes place. Thus, when changes in toner material are effected, resulting in changes in dispenser rate, compensation for these effects may be made in a simple uncomplicated manner.